1. Field of the Invention
The present invention relates generally to Wankel type rotary engines, and more particularly, to an improved rotor construction and intake charge entry and distribution port configuration providing substantially uniform intake charge cooling across the rotor. Improved heat transfer devices are provided within rotor cavities and a novel seal lubricating arrangement is included.
2. Description of the Prior Art
Wankel type rotary engines are commonly used in many applications including automobiles, hybrid automobiles, recreational vehicles, and portable power plants. These engines operate according to a four stroke process having four cycles including intake, compression, expansion, and exhaust. FIGS. 1A through 1D illustrate side views of a typical prior art rotary engine engaged in the four cycles of operation.
As shown in FIGS. 1A through 1D, the engine typically includes a rotor 102 having three flanks forming combustion surfaces 101a, 101b, and 101c located between three apexes, and a crankshaft 104 having an eccentric 105 disposed within a rotor housing 106. Rotor housing 106, which has an inner surface 107 in the shape of a peritrochoid curve, includes an intake port 108 and an exhaust port 110. End plates (not shown) are affixed to ends of rotor housing 106 to form a closed chamber 112.
The rotor 102 engages eccentric 105 of the crankshaft via a rotor bearing (not shown) which typically includes an inner bearing race, an outer bearing race, and a plurality of roller bearings. Rotor 102, which drives crankshaft 104, includes a rotor gear 114 which engages a stationary gear 116 affixed to an end plate (not shown). The rotor revolves at one third the speed of the crankshaft and the spark plugs fire once per revolution of the crankshaft.
In operation, as rotor 102 rotates, the three combustion surfaces 101a, 101b, and 101c serve to variously combine with the inner surface of housing 106 to variously define an intake volume, a compression volume, an ignition volume, and an exhaust volume of closed chamber 112.
FIG. 1A depicts in particular the intake cycle during which intake port 108 is open and the rotor surface 101a defines an intake volume 109 of the closed chamber which increases in volume to draw charge there-into from an external source such as a carburetor (not shown). FIG. 1B specifically depicts the engine during the compression cycle in which the compression volume 111 is decreased to compress the charge. FIG. 1C shows at 113 the ignition cycle during which compressed charge is ignited by a spark to provide a force pushing the rotor around as the ignited charge expands. FIG. 1D depicts at 115 the exhaust cycle wherein the contents of the exhaust volume is cleared via exhaust port 110 to prepare the engine for another cycle. Note that as the rotor 102 turns within the housing 106, the rotor surfaces 101b and 101c likewise define intake, compression, combustion, and exhaust cycles.
FIG. 2A shows an exploded perspective view of the prior art engine of FIG. 1A. Rotor 102 includes a central hub 117 having a central axis A, rotor flanks 118, and flank supports 119 extending transverse to the central axis and joining the hub to the flanks. As depicted, the engine further includes a first end plate 122 and a second end plate 124 for attachment to first and second ends of rotor housing 106 to form the closed chamber 112.
Housing 106 includes spark plug holes 126 bored there through to receive spark plugs (not shown) used for ignition. Housing 106 further includes peripheral ports 128 which are open to chamber 112 and allow charge to flow into the chamber as explained further below.
Rotor 102 includes large flow passages 130, located between flank supports 119, which allow charge to flow through the rotor, parallel to crankshaft 104 (FIG. 1A), from first end plate 122 to second end plate 124 as explained further below. Because rotor 102 includes flow passages 130, the rotor lacks structural support material in locations where support could most effectively add strength to the rotor. To compensate and strengthen the rotor, more material must be added to the rotor elsewhere thereby detrimentally increasing its weight. The weight of the rotor is critical because it effects the weight of crankshaft 104 (FIG. 1A), the amount of counterweight required, the size of the rotor bearing (not shown), and the overall structure of the engine.
First end plate 122 includes a fuel/air inlet 132 which receives charge from an external source (not shown). First end plate 122 also includes a first port 134 formed by a cavity, or slot, on an inner surface 133 of the first end plate and open at various times to flow passages 130 and interior 123 of the rotor 102. First port 134 is in communication with inlet 132 and allows for flow of charge from the external source into flow passages 130 of rotor 102.
Second end plate 124 includes a distribution chamber 135 formed by a cavity in an inner surface 137 of the second end plate and open to chamber 112. Distribution chamber 135 has a side port 136 defined by the edges of distribution chamber 135 and a dashed line 141. Side port 136 communicates with closed chamber 112 subject to obstruction by rotor 102. The remaining portion of distribution chamber 135, excluding side port 136, is identical to first port 134 and communicates with flow passages 130, interior 123 of rotor 102, and passage 152. Second end plate 124 does not include a fuel/air inlet. Side port 136 receives the charge from the first port 134 of the first end plate via flow passages 130 of the rotor and distribution chamber 135. Distribution chamber 135 is in communication with a port outlet 138 formed on the inner surface of a flange of the second end plate. Outlet 138 provides passage of charged air from distribution chamber 135 to a peripheral port inlet 140 of rotor housing 106 when second end plate 124 is affixed to rotor housing 106.
In the depicted engine, intake charge is received solely via fuel/air inlet 132 of the first end plate 122. The engine therefore uses a single entry port configuration in which cooling charge enters the engine from an external source via one side of the engine only. The port configuration is formed essentially by inlet 132, first port 134, flow passages 130 of the rotor, distribution chamber 135, side port 136, side port outlet 138, peripheral port inlet 140, and peripheral ports 128. The exact flow path of charge through the port configuration of the engine varies with the position and rotational speed of rotor 102. Flow paths 142, 144, and 146 illustrate the flow of charge through the engine.
According to flow path 142, charge flows: (1) from an external source (not shown) through fuel/air inlet 132 of first end-housing 122 to first port 134; (2) through flow passages 130 of the rotor parallel to crankshaft 104 (FIG. 1A); (3) to distribution chamber 135 of the second end plate; and (4) into closed chamber 112 via flow path 144 and/or flow path 146. Charge flows from side port 136 directly into chamber 112 subject to partial obstruction by rotor 102. Charge also flows from distribution chamber 135 along another path 146 into closed chamber 112 via passage 152, side port outlet 138, peripheral port inlet 140, and peripheral ports 128.
Because charge enters the engine through first end plate 122 only, via first port 134 and flows through rotor 102, the side of the rotor adjacent end plate 122 forms a charge entering end of the rotor. Also, because cooling charge does not enter side port 136 directly from an external source, the second end plate is referred to as a charge exiting side of the rotor. As the charge is passed through flow passages 130 of the rotor, via flow path 142, it absorbs heat and its cooling ability is diminished on the exiting side of the rotor. Thus, the rotor temperature at the exiting side of the engine, adjacent second end plate 124, could be as much as 100.degree. F. hotter than the temperature at the entering side of the rotor adjacent first end plate 122.
FIG. 2B shows an axial cross sectional view of the prior art engine taken through the peripheral ports 128. Rotor 102 includes side seals 149 extending from rotor flanks 118 for sealing the sides of the rotor to inner walls of the first and second end plates 122 and 124. A passage 150, formed in first end plate 122, provides for communication between fuel/air inlet 132 and first port 134. First port 134 communicates directly with flow passages 130 of rotor 102 and is isolated from direct exposure to chamber 112 by the flanks and side seals of rotor 102. A passage 152, formed in second end plate 124, provides a communicating path between distribution chamber 135 and side port outlet 138 and a passageway 154, formed in housing 106, connects inlet 140 and peripheral ports 128. According to charge flow path 144, charge flows from side port 136 directly into closed chamber 112. According to charge flow path 146, charge flows from distribution chamber 135 into closed chamber 112 via passages 152 and 154.
As mentioned, eccentric 117 of crank shaft 104 is rotatably coupled to rotor 102 via rotor bearing 158 which typically includes a plurality of roller bearing members secured between an inner bearing race and an outer bearing race. The bearing 158 in this type of prior art charge cooled engine does not run in oil and therefore must use a roller bearing as distinct from a hydro-dynamically supported bearing.
If one side of rotor 102 is even slightly hotter than the opposite side (as little as 10.degree. F.), the bearing race of the bearing 158 on the hotter side of the rotor will be slightly larger due to the thermal expansion differential across the bearing. Because the temperature at the exiting side of the depicted engine, adjacent second end plate 124, could actually be as much as 100.degree. F. hotter than at the entering side of the engine adjacent first end plate 122, the bearing race will be caused to taper axially and cause end-loading of the bearing rollers that will greatly reduce the load-carrying capacity and life of bearing 158. In addition, this coning effect will cause the rotor to thrust to one side and substantially increase the friction and wear on rotor 102 and particularly on side seals 149 of the rotor. The side thrust can also result in side gouging of the inner walls 133 and 137 of the end plates 122 and 124 (FIG. 2A) of housing 106. The coning effect also limits maximum rotational speed of the rotor under high compression loads.
Moreover, in the prior art engine, the quick passage of charge across rotor 102 provides limited opportunity for overall cooling of the rotor. Therefore, the temperature of rotor bearing 158 may reach as high as 400.degree. F. , the point at which lubrication begins to fail and metallurgical change (grain growth) begins to occur in the bearing material. Intake charge may also pass through rotor 102 during only a portion of the intake cycle and thus, because the engine may starve for part of the intake cycle, it may be necessary to provide an additional charge flow path by passing charge through eccentric 105 of crankshaft 104. In so doing, one side of eccentric 105 may be cooled more than the other side. This effect causes an additional asymmetric cooling problem in addition to reducing the amount of charge available for overall cooling of the rotor.
Furthermore, the absence of an efficient support structure in this cross-flow arrangement leads to placement of much of the structural support of rotor 102 between the rotor face and the bearing at a point where they are in close proximity. This allows a large heat flux to accumulate at a point where there is little surface area to disperse the heat.
Another problem existing in prior art rotary engines relates to the manner in which lubricant is applied to the rubbing surfaces and seals of the engine.
Historically, all two stroke engines and rotary engines have injected oil into the air stream as a means of lubricating the rings or seals. In particular, all charge cooled rotary engines have lubricated the seals entirely by either injecting lubricating oil into the air stream or mixing oil with the fuel which has the same result.
When oil enters the air stream, it becomes problematic whether much of it actually serves to lubricate the engine. For the most part, the oil remains suspended in the charge and is partially burned along with the gasoline. It is a major source of exhaust burned and unburned particulates in a two-stroke engine operation.
Practical two stroke engines must inject oil into the air stream. Subsequently, this oil becomes particulates which have recently been established as carcinogenic and mutagenic. Moreover, unlike gasoline which, given time, does not leave the water to enter the air, those oil particulates that do not remain suspended, enter the water and remain where they can do the most environmental damage. Even if the two stroke engine becomes very fuel efficient, though that is unlikely, this problem will remain a fundamental part of any reasonably priced two stroke engine. Existing four stroke rotary engines, such as those manufactured by Mazda, OMC, RPI, and Norton all inject oil into the air stream (generally lower quantities than two-strokes). Four stroke piston engines do not inject oil but are impractical candidates for use in the weight and volume-sensitive recreational vehicles, hybrid automobiles and portable power plants.
Burtis (U.S. Pat. No. 5,203,307) discloses a rotary engine including an improved oil lubricating system for lubricating apex seals of a rotor. The lubricating system described by Burtis contrasts with prior conventional methods of lubricating apex seals by injecting oil into the air intake using a separate oil pump system. Such conventional systems resulted in poor lubrication results, carbon formation on the rotor face and engine housing, and increased pollution from oil combustion in the combustion chamber.
The oil lubricating system disclosed in Burtis includes: an axial crankshaft passageway formed in a crankshaft into which oil flows; a lobe passageway formed in the lobe, or eccentric, of the shaft in communication at one end thereof with the crankshaft passageway and at the other end thereof with a rotor roller bearing; and a rotor passageway extending through the rotor to the apex of the rotor. During operation of the engine system, oil flows through the crankshaft passageway into the lobe passageway and to the rotor roller bearing to lubricate the roller bearing. Oil then flows from the roller bearing flows through an open race and into the rotor oil passageway to lubricate apex seals disposed at the apexes of the rotor. A small amount of oil flows through the passageway to lubricate the apex seals from the inside of the rotor.
One problem with the rotary engine described by Burtis is that lubrication is not efficiently provided to side seals of the rotor. Another problem with the rotary engine described by Burtis is that oil is not evenly distributed from the rotor passageway, that is from the apex of the rotor, to the interior wall of the rotor housing because, fuel/air charge is injected into the rotor housing from one side only, and therefore, there is an unbalanced flow of charge forcing the lubricant to flow unevenly.
Still another problem with conventional rotary engines relates to the ability of the engine to transfer heat away from the engine parts subjected to the highest temperatures, such as the apex seals, side seals, and rotor bearing structure. Charge-cooled rotary engines have historically been limited in power output by a need to transfer sufficient heat away from the apex seals while not transferring too much heat into the rotor bearing. This delicate balance has required designers of rotary engines to operate within narrow boundaries of RPM and horse power (HP). Because heat transfer is a function of rotor RPM and air-flow, it is not possible to operate a typical charge-cooled engine at substantial power when operating at low RPM where intake air flow is also lower.
What is needed is a means for providing sufficient and uniform charge cooling in a rotary engine on both sides of the rotor in order to substantially reduce problems associated with asymmetric cooling, including end loading of rotor bearings, side thrusting of the rotor, and the need to pass charge through the eccentric. Further needed is a charge cooled rotary engine having a rotor of reduced weight and uncompromised strength.
Another need exists for a means for providing effective and even lubrication of the seals and rubbing surfaces of the engine without requiring that substantial amounts of lubricant enter the charge flow stream as it passes through the engine.
Further needed is a rotary engine having improved heat transfer characteristics.